The present invention relates to digital communication networks and more particularly, to the configuration of network nodes interconnected in ring topologies.
Increasingly, fiber optic technology is being deployed to answer the need to accommodate increasing volumes of Internet traffic including web-based electronic commerce, voice over IP, (VoIP), video over IP, and virtual private networking (VPN). In many cases, fiber optic technology has been adapted for use on the Internet by exploiting network topologies and protocols that were themselves originally developed for use in carrying multiple streams of telephony traffic using time domain multiplexing (TDM) technology.
In particular, many metropolitan and backbone networks providing IP data communication services rely on the SONET protocol developed for voice telephony traffic to provide transport services through optical fiber-based networking equipment. To provide reliability, SONET nodes are often arranged in a ring configuration where one or more rings interconnect a series of fiber optic nodes. The ring configuration provides survivability and robustness in that if a ring segment between two nodes fails, traffic may be sent the other way around the ring, or shifted to a different parallel ring if necessary.
This architecture is, however, not ideal for modern Internet traffic requirements. The multiplexed SONET data streams each have fixed bandwidth and there is no opportunity to take full advantage of statistical multiplexing, i.e., allocate bandwidth currently left unused by some services to other services experiencing peak requirements. SONET architecture therefore does not fully exploit the advantages of packet-based network networking. Furthermore, a very large percentage of the bandwidth in a SONET ring is left unused in order to implement the ring self-healing capabilities described above.
In order to address these concerns and provide other capabilities, Cisco Systems, Inc., has developed Dynamic Packet Transport (DPT) and Spatial Reuse Protocol (SRP) for use with ring-based media. These solutions combine the bandwidth efficiency and ready compatibility with Internet services of IP routing techniques with the very large bandwidth and self-healing capabilities of fiber rings. Although SONET framing may be used, TDM timeslots are not reserved for particular services or connections. Instead, DPT and SRP divide the available bandwidth among nodes and services on a real-time basis in an optimal and fair fashion. Furthermore, instead of reserving an entire ring for protection, both rings of a pair may be concurrently utilized to pass working traffic.
A DPT ring pair consists of two counter-rotating fibers, each of which can be concurrently utilized to pass both data and control packets. To distinguish between the two rings, one is referred to as the “inner” and the other “outer” ring. Data packets for a particular bi-directional connection travel on one ring and corresponding control packets travel in the opposite direction on the other ring. Packets are stripped from the ring by the destination station.
FIG. 1 depicts a simplified representation of a network employing a bi-directional dual counter-rotating ring topology such as employed by DPT/SRP. Six nodes, numbered I–VI are interconnected. Each of the six depicted nodes has two sides labeled “A” and “B.” Each A side is equipped with an input for the outer ring and an output for the inner ring whereas each B side is equipped with an input for the inner ring and an output for the outer ring.
A practical difficulty arises in connecting a new node to this network in that there will be two fiber pairs available at the node site and the installer will have to determine which pair to connect to the A side and which pair to connect to the B side. Unless this is done to match the existing connections in the ring, the ring will not operate properly.
In effect, a node may be said to have one of two “polarities.” The polarity identifies which ring is “inner” and which ring is “outer” according to the DPT/SRP protocol. In FIG. 1, the polarity can be reversed by flipping each node's B side and A side. When a new double ring network is set up, a polarity must somehow be determined and observed by all the nodes. When a new node joins an existing ring, it must adopt a polarity that will match the polarities of the other nodes on the ring. In, for example, a metropolitan network, the nodes will be widely dispersed and it may be difficult to determine which fiber pair should be connected to which side of the node to establish or conform to network polarity.
What is needed are systems and methods for simplifying the establishment and maintenance of network polarity in double ringed topologies.